Generic ground milling machines, such as road milling machines, recyclers, stabilizers or surface miners, are used for street and roadway construction or for exploitation of mineral resources. They comprise a machine frame supported by undercarriages, on which a milling drum rotatably mounted in a milling drum box is arranged. By rotation of the milling drum fitted with milling tools, the ground milling machines remove the ground up to a desired depth in the working direction. The undercarriages of the ground milling machines may be crawler tracks as well as wheels. Usually, they are connected to the machine frame via height-adjustable lifting columns. By height adjustment of the lifting columns, the entire machine frame together with the milling drum box is raised or lowered, and thereby the milling depth of the milling drum can also be adjusted. Further, it is possible to adjust individual lifting columns, the two front-side or the two rear-side lifting columns together, for adjusting the longitudinal inclination of the ground milling machine (i.e., the horizontal inclination in the milling direction) and/or the two lifting columns located on the right or on the left with respect to the longitudinal center of the machine, for adjusting the transverse inclination of the ground milling machine (i.e., the horizontal inclination transversely to the milling direction). Typically, a control unit is provided that controls, inter alia, said height adjustment according to the input of the driver of the ground milling machine.
Usually, the milling drum is rotatably mounted in a milling drum box that is typically attached to the machine frame and, in particular, moves up and down with said frame when the height of the machine frame is adjusted via the lifting columns of the undercarriages. The milling drum box encloses the milling drum in the type of a hood and is open towards the ground. Usually, it comprises two side plates that confine the milling drum box in parallel to the working direction. The side plates are generally mounted so as to be movable relative to the machine frame, and are, in particular, height-adjustable in the vertical direction. For this purpose, at least one actuator is hinged at the side plate, which actuator can drive the height adjustment movement of the side plate. This actuator may further be arranged on the machine frame or on the milling drum box, for example. Ideally, two actuators are provided per side plate, specifically, one actuator positioned in the front and one actuator positioned in the rear in the working direction, which connect the machine frame and/or the milling drum box to the side plate and can move the latter up and down. Such an arrangement may be provided for the right-hand side plate as well as for the left-hand side plate viewed in the milling direction. As an alternative to hydraulic cylinders, electrical actuators, in particular electrical linear motors/actuators, may also be employed. During working operation, the side plates rest on the ground and slide over the latter by means of sliding shoes. Together with the other parts of the milling drum box, they prevent milled material from being thrown out of the milling track.
At the beginning of a milling process, the milling drum has to be lowered to a desired milling depth. This usually takes place by means of an automatic mechanism that adjusts the lifting columns of the undercarriages of the ground milling machine and/or the axis of rotation of the milling drum in the milling drum box, until a desired value is achieved. Often, however, the automatic system adjusts, for instance, the at least one front-side lifting column only, and thereby, after bringing the milling drum in place, the ground milling machine or the machine frame thereof, respectively, will be oriented obliquely to the ground. However, since, for instance, for reasons of machine stability and the full use of the machine weight as a counter-weight for the operation of the milling drum, it is beneficial if the ground milling machine, respectively the machine frame thereof and/or the milling drum box is arranged as parallel as possible to the ground during operation, the driver of the ground milling machine has to manually correct the height of the at least one rear-side lifting column until the machine frame and thus the milling drum box are parallel to the ground by visual estimate.
DE 10 2006 062 129 A1 discloses a ground milling machine of the generic type, in which for detecting the orientation of the machine, sensors are provided that detect the distance of the machine to the ground at different positions as well as the depth of the milling track. These values also allow for determining the position of the machine relative to the ground, so that said machine can be positioned in parallel.
From DE 11 2012 005 425 T5, it is known to provide side plate sensors to be contacted by the ground. Here, the side plate sensors are located directly in the working area of the milling drum and thus in an area affected by dirt. This may be disadvantageous for the functioning of these side plate sensors.
It is the object of the present invention to provide an option by means of which a ground milling machine or the milling drum box thereof, respectively, can be brought into a desired position relative to the ground, for instance, in parallel, without this being effected by manual adjustment using the driver's visual estimate. It is therefore another object to assist the driver of the ground milling machine when positioning the machine. At the same time, dirt in the area of the milling drum box should affect these adjustments as little as possible.